From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sender4-op-o15.zoho.com (sender4-op-o15.zoho.com [136.143.188.15]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 46D4E3B27D0; Mon, 11 May 2026 08:47:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=pass smtp.client-ip=136.143.188.15 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778489255; cv=pass; b=VbdkHWM+FsNHX0MGIErs+Kci2tx9feMvBXssr5lTnmYkGWQInPS+7ibnDHUkzZLgPlB8wirFHhHnZSyO62Akg5RAFCesxm01/9/Jow2/xnmYZ99IuUvJpzzZhhH70COV3JtRmL4Xv5nIROh5n6yc+2KSFtEoP6A6dxuuWHPPdh4= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778489255; c=relaxed/simple; bh=9+r0lXSAyXV2axYn2KPYR7C9ZTyqeMxFEhiqo0oAZvk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RH6sKICgY3iXRM1r6KeKUgqERV7SDzzsRhb77Xx2TsXDqCzqZ8Q5PimNOOUlSv1P+cTOgrGeHJ80OkIg6sLCTIiAhI5rqWALErDDE5USa9wcYw9Qlsg4En43X04zK6WINJwbeXJuKF1j3pOFwPlzGbwIFlJQCRgOsT0ta9TRKLk= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.beauty; spf=pass smtp.mailfrom=linux.beauty; dkim=pass (1024-bit key) header.d=linux.beauty header.i=me@linux.beauty header.b=nUXvM8ZR; arc=pass smtp.client-ip=136.143.188.15 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.beauty Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.beauty Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.beauty header.i=me@linux.beauty header.b="nUXvM8ZR" ARC-Seal: i=1; a=rsa-sha256; t=1778489047; cv=none; d=zohomail.com; s=zohoarc; b=WyoS015f3djO5Y4dPKyoo2z5zTgdpeR9xI8K1zEiZkliUlo6KwM+NCO/F8PAO+rJpZc0dE0IWU+I/ZbFNnM+mOqdbFCdDp2VFcTWHCABrkpcERo6Br7K1uDXicm6dr19sxSV96bxDusQ9zqdFyMVad4AKZxm4o1+VtMXgGzfFnI= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1778489047; h=Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:In-Reply-To:MIME-Version:Message-ID:References:Subject:Subject:To:To:Message-Id:Reply-To; bh=aVVT3ps1SdnisVf/bD8Ws+M3UP7WXtuL/UZyauh6zA8=; b=LVVWsztFjRqId3BBkzbXKcw4aaT2pR75mwEVaeMcluVrL+Jj6WipGc4dtk91WP8dgqM0hL5xgt99Hjk/zuSPAXaNE1HJQjkqMM+wiC6ERdfkGxKtoHawBeBOKBR1s+jMFJOV3Eo4Ejbl5o+dGX8mE47sUB0Ub5q2wCHz4c+xjYY= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass header.i=linux.beauty; spf=pass smtp.mailfrom=me@linux.beauty; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1778489047; s=zmail; d=linux.beauty; i=me@linux.beauty; h=From:From:To:To:Cc:Cc:Subject:Subject:Date:Date:Message-ID:In-Reply-To:References:MIME-Version:Content-Transfer-Encoding:Message-Id:Reply-To; bh=aVVT3ps1SdnisVf/bD8Ws+M3UP7WXtuL/UZyauh6zA8=; b=nUXvM8ZRK+dzw0bset72KC3dWKBot9hlgSJEeaExS8y8eRePJakBfC4VRiYhaqC5 9uR0jFqDFLVq5fG7jy2I9EvQJ7bzGrWZ0/FFsw/88sQDctlzz367mG+h5eZDdatLx08 mPau/xvOuULLdimv0MuwdHjd/KCgldlLScDBo090= Received: by mx.zohomail.com with SMTPS id 1778489044493301.0632124891529; Mon, 11 May 2026 01:44:04 -0700 (PDT) From: Li Chen To: Zhang Yi , Theodore Ts'o , Andreas Dilger , Baokun Li , Jan Kara , Ojaswin Mujoo , "Ritesh Harjani (IBM)" , Zhang Yi , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , linux-trace-kernel@vger.kernel.org Subject: [RFC v7 7/7] ext4: fast commit: export snapshot stats in fc_info Date: Mon, 11 May 2026 16:43:02 +0800 Message-ID: <20260511084304.1559557-8-me@linux.beauty> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260511084304.1559557-1-me@linux.beauty> References: <20260511084304.1559557-1-me@linux.beauty> Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-ZohoMailClient: External Snapshot-based fast commit can fall back when the commit-time snapshot cannot be built (e.g. extent status cache misses). It is useful to quantify the updates-locked window and to see why snapshotting failed. Add best-effort snapshot counters to the ext4 superblock and extend /proc/fs/ext4//fc_info to report the number of snapshotted inodes and ranges, snapshot failure reasons, and the average/max time spent with journal updates locked. Signed-off-by: Li Chen --- Changes in v7: - Address Sashiko review by using READ_ONCE() + div64_u64() for the fc_info lock_updates average. Changes in v6: - Start consuming locked_ns in fc_info, so this patch intentionally moves lock_updates_ns_{total,max,samples} accounting here. - Guard the tracepoint call with trace_ext4_fc_lock_updates_enabled() and use trace_call__ext4_fc_lock_updates() to avoid the double static_branch at the guarded call site. - Keep the stats unconditionally while avoiding extra tracepoint overhead when ext4_fc_lock_updates is disabled. fs/ext4/ext4.h | 31 +++++++++++++++++ fs/ext4/fast_commit.c | 78 +++++++++++++++++++++++++++++++++++++------ fs/ext4/super.c | 1 + 3 files changed, 100 insertions(+), 10 deletions(-) diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index df30f8705c98..3457b4950c02 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1550,6 +1550,36 @@ struct ext4_orphan_info { * file blocks */ }; +/* + * Ext4 fast commit snapshot statistics. + * + * These are best-effort counters intended for debugging / performance + * introspection; they are not exact under concurrent updates. + */ +struct ext4_fc_snap_stats { + u64 lock_updates_ns_total; + u64 lock_updates_ns_max; + u64 lock_updates_samples; + + u64 snap_inodes; + u64 snap_ranges; + + u64 snap_fail_es_miss; + u64 snap_fail_es_delayed; + u64 snap_fail_es_other; + + u64 snap_fail_inodes_cap; + u64 snap_fail_ranges_cap; + u64 snap_fail_nomem; + u64 snap_fail_inode_loc; + + /* + * Missing inode snapshots during log writing should never happen. + * Keep this counter to help catch unexpected regressions. + */ + u64 snap_fail_no_snap; +}; + /* * fourth extended-fs super-block data in memory */ @@ -1824,6 +1854,7 @@ struct ext4_sb_info { struct mutex s_fc_lock; struct buffer_head *s_fc_bh; struct ext4_fc_stats s_fc_stats; + struct ext4_fc_snap_stats s_fc_snap_stats; tid_t s_fc_ineligible_tid; #ifdef CONFIG_EXT4_DEBUG int s_fc_debug_max_replay; diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c index c24984d8df83..1dfcccf4179e 100644 --- a/fs/ext4/fast_commit.c +++ b/fs/ext4/fast_commit.c @@ -874,13 +874,17 @@ static int ext4_fc_write_inode(struct inode *inode, u32 *crc) int inode_len; int ret; - if (!snap) + if (!snap) { + EXT4_SB(inode->i_sb)->s_fc_snap_stats.snap_fail_no_snap++; return -ECANCELED; + } src = snap->inode_buf; inode_len = snap->inode_len; - if (!src || inode_len == 0) + if (!src || inode_len == 0) { + EXT4_SB(inode->i_sb)->s_fc_snap_stats.snap_fail_no_snap++; return -ECANCELED; + } fc_inode.fc_ino = cpu_to_le32(inode->i_ino); tl.fc_tag = cpu_to_le16(EXT4_FC_TAG_INODE); @@ -915,8 +919,10 @@ static int ext4_fc_write_inode_data(struct inode *inode, u32 *crc) struct ext4_extent *ex; struct ext4_fc_range *range; - if (!snap) + if (!snap) { + EXT4_SB(inode->i_sb)->s_fc_snap_stats.snap_fail_no_snap++; return -ECANCELED; + } list_for_each_entry(range, &snap->data_list, list) { if (range->tag == EXT4_FC_TAG_DEL_RANGE) { @@ -977,6 +983,8 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode, int *snap_err) { struct ext4_inode_info *ei = EXT4_I(inode); + struct ext4_fc_snap_stats *stats = + &EXT4_SB(inode->i_sb)->s_fc_snap_stats; ext4_lblk_t start_lblk, end_lblk, cur_lblk; unsigned int nr_ranges = 0; @@ -1004,11 +1012,13 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode, u64 remaining = (u64)end_lblk - cur_lblk + 1; if (!ext4_es_lookup_extent(inode, cur_lblk, NULL, &es, NULL)) { + stats->snap_fail_es_miss++; ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_ES_MISS); return -EAGAIN; } if (ext4_es_is_delayed(&es)) { + stats->snap_fail_es_delayed++; ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_ES_DELAYED); return -EAGAIN; @@ -1023,6 +1033,7 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode, } if (nr_ranges_total + nr_ranges >= EXT4_FC_SNAPSHOT_MAX_RANGES) { + stats->snap_fail_ranges_cap++; ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_RANGES_CAP); return -E2BIG; @@ -1030,6 +1041,7 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode, range = kmem_cache_alloc(ext4_fc_range_cachep, GFP_NOFS); if (!range) { + stats->snap_fail_nomem++; ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_NOMEM); return -ENOMEM; } @@ -1057,6 +1069,7 @@ static int ext4_fc_snapshot_inode_data(struct inode *inode, range->len = max; } else { kmem_cache_free(ext4_fc_range_cachep, range); + stats->snap_fail_es_other++; ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_ES_OTHER); return -EAGAIN; } @@ -1080,6 +1093,8 @@ static int ext4_fc_snapshot_inode(struct inode *inode, unsigned int *nr_rangesp, int *snap_err) { struct ext4_inode_info *ei = EXT4_I(inode); + struct ext4_fc_snap_stats *stats = + &EXT4_SB(inode->i_sb)->s_fc_snap_stats; struct ext4_fc_inode_snap *snap; int inode_len = EXT4_GOOD_OLD_INODE_SIZE; struct ext4_iloc iloc; @@ -1090,6 +1105,7 @@ static int ext4_fc_snapshot_inode(struct inode *inode, ret = ext4_get_inode_loc_noio(inode, &iloc); if (ret) { + stats->snap_fail_inode_loc++; ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_INODE_LOC); return ret; } @@ -1101,6 +1117,7 @@ static int ext4_fc_snapshot_inode(struct inode *inode, snap = kmalloc(struct_size(snap, inode_buf, inode_len), GFP_NOFS); if (!snap) { + stats->snap_fail_nomem++; ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_NOMEM); brelse(iloc.bh); return -ENOMEM; @@ -1125,6 +1142,8 @@ static int ext4_fc_snapshot_inode(struct inode *inode, list_splice_tail_init(&ranges, &snap->data_list); ext4_fc_unlock(inode->i_sb, alloc_ctx); + stats->snap_inodes++; + stats->snap_ranges += nr_ranges; if (nr_rangesp) *nr_rangesp = nr_ranges; return 0; @@ -1234,6 +1253,7 @@ static int ext4_fc_snapshot_inodes(journal_t *journal, struct inode **inodes, alloc_ctx = ext4_fc_lock(sb); list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) { if (i >= inodes_size) { + sbi->s_fc_snap_stats.snap_fail_inodes_cap++; ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_INODES_CAP); ret = -E2BIG; @@ -1259,6 +1279,7 @@ static int ext4_fc_snapshot_inodes(journal_t *journal, struct inode **inodes, continue; if (i >= inodes_size) { + sbi->s_fc_snap_stats.snap_fail_inodes_cap++; ext4_fc_set_snap_err(snap_err, EXT4_FC_SNAP_ERR_INODES_CAP); ret = -E2BIG; @@ -1302,6 +1323,7 @@ static int ext4_fc_perform_commit(journal_t *journal, tid_t commit_tid) { struct super_block *sb = journal->j_private; struct ext4_sb_info *sbi = EXT4_SB(sb); + struct ext4_fc_snap_stats *snap_stats = &sbi->s_fc_snap_stats; struct ext4_inode_info *iter; struct ext4_fc_head head; struct inode *inode; @@ -1364,8 +1386,13 @@ static int ext4_fc_perform_commit(journal_t *journal, tid_t commit_tid) return ret; ret = ext4_fc_alloc_snapshot_inodes(sb, &inodes, &inodes_size); - if (ret) + if (ret) { + if (ret == -E2BIG) + snap_stats->snap_fail_inodes_cap++; + else if (ret == -ENOMEM) + snap_stats->snap_fail_nomem++; return ret; + } /* Step 4: Mark all inodes as being committed. */ jbd2_journal_lock_updates(journal); @@ -1386,12 +1413,15 @@ static int ext4_fc_perform_commit(journal_t *journal, tid_t commit_tid) ret = ext4_fc_snapshot_inodes(journal, inodes, inodes_size, &snap_inodes, &snap_ranges, &snap_err); jbd2_journal_unlock_updates(journal); - if (trace_ext4_fc_lock_updates_enabled()) { - locked_ns = ktime_to_ns(ktime_sub(ktime_get(), lock_start)); - trace_ext4_fc_lock_updates(sb, commit_tid, locked_ns, - snap_inodes, snap_ranges, ret, - snap_err); - } + locked_ns = ktime_to_ns(ktime_sub(ktime_get(), lock_start)); + snap_stats->lock_updates_ns_total += locked_ns; + snap_stats->lock_updates_samples++; + if (locked_ns > snap_stats->lock_updates_ns_max) + snap_stats->lock_updates_ns_max = locked_ns; + if (trace_ext4_fc_lock_updates_enabled()) + trace_call__ext4_fc_lock_updates(sb, commit_tid, locked_ns, + snap_inodes, snap_ranges, + ret, snap_err); kvfree(inodes); if (ret) return ret; @@ -2667,11 +2697,23 @@ int ext4_fc_info_show(struct seq_file *seq, void *v) { struct ext4_sb_info *sbi = EXT4_SB((struct super_block *)seq->private); struct ext4_fc_stats *stats = &sbi->s_fc_stats; + struct ext4_fc_snap_stats *snap_stats = &sbi->s_fc_snap_stats; + u64 lock_avg_ns = 0; + u64 lock_updates_samples; + u64 lock_updates_ns_total; + u64 lock_updates_ns_max; int i; if (v != SEQ_START_TOKEN) return 0; + lock_updates_samples = READ_ONCE(snap_stats->lock_updates_samples); + lock_updates_ns_total = READ_ONCE(snap_stats->lock_updates_ns_total); + lock_updates_ns_max = READ_ONCE(snap_stats->lock_updates_ns_max); + if (lock_updates_samples) + lock_avg_ns = div64_u64(lock_updates_ns_total, + lock_updates_samples); + seq_printf(seq, "fc stats:\n%ld commits\n%ld ineligible\n%ld numblks\n%lluus avg_commit_time\n", stats->fc_num_commits, stats->fc_ineligible_commits, @@ -2682,6 +2724,22 @@ int ext4_fc_info_show(struct seq_file *seq, void *v) seq_printf(seq, "\"%s\":\t%d\n", fc_ineligible_reasons[i], stats->fc_ineligible_reason_count[i]); + seq_printf(seq, + "Snapshot stats:\n%llu inodes\n%llu ranges\n%lluus lock_updates_avg\n%lluus lock_updates_max\n", + snap_stats->snap_inodes, snap_stats->snap_ranges, + div_u64(lock_avg_ns, 1000), + div_u64(lock_updates_ns_max, 1000)); + seq_printf(seq, + "Snapshot failures:\n%llu es_miss\n%llu es_delayed\n%llu es_other\n%llu inodes_cap\n%llu ranges_cap\n%llu nomem\n%llu inode_loc\n%llu no_snap\n", + snap_stats->snap_fail_es_miss, + snap_stats->snap_fail_es_delayed, + snap_stats->snap_fail_es_other, + snap_stats->snap_fail_inodes_cap, + snap_stats->snap_fail_ranges_cap, + snap_stats->snap_fail_nomem, + snap_stats->snap_fail_inode_loc, + snap_stats->snap_fail_no_snap); + return 0; } diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 3c869f0001c5..f1f8819a2a23 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -4544,6 +4544,7 @@ static void ext4_fast_commit_init(struct super_block *sb) sbi->s_fc_ineligible_tid = 0; mutex_init(&sbi->s_fc_lock); memset(&sbi->s_fc_stats, 0, sizeof(sbi->s_fc_stats)); + memset(&sbi->s_fc_snap_stats, 0, sizeof(sbi->s_fc_snap_stats)); sbi->s_fc_replay_state.fc_regions = NULL; sbi->s_fc_replay_state.fc_regions_size = 0; sbi->s_fc_replay_state.fc_regions_used = 0; -- 2.53.0